The present invention relates to a liquid jetting head, a method of manufacturing the same, and a liquid jetting apparatus such as a recording head for an ink jet recording apparatus, an electrode member ejection head for an electrode forming apparatus, an organic substance jetting head for a bio-chip manufacturing apparatus, or the like, in which liquid is ejected by deformation of piezoelectric elements formed on a surface of a diaphragm formed as a part of pressure generating chambers communicating with nozzle orifices from which liquid is ejected.
For example, a serial printing type ink jet recording apparatus, which is one kind of the liquid jetting apparatus, including either one of two types of liquid jetting heads (hereinafter, referred as xe2x80x9cink jet recording headsxe2x80x9d) have been put into practical use as the ink jet recording head in which a diaphragm formed as a part of pressure generating chambers communicating with nozzle orifices is deformed by piezoelectric elements to pressurize liquid (hereinafter, referred as xe2x80x9cinkxe2x80x9d) in the pressure generating chambers to thereby eject ink drops from the nozzle orifices. One type of ink recording head uses a longitudinal vibration mode piezoelectric actuator that expands and contracts in an axial direction of the piezoelectric elements. The other type of ink recording head uses a flexure vibration mode piezoelectric actuator.
The former has an advantage in that a head adapted to high-density printing can be manufactured because the volume of the pressure generating chambers can be changed by the diaphragm abutting on end surfaces of the piezoelectric elements. In the former, there are, however, required the process of cutting a piezoelectric element into the form of the teeth of a comb in accordance with the pitch of arrangement of the nozzle orifices, and the work of positioning the thus cut piezoelectric elements to be fixed to the pressure generating chambers respectively.
On the other hand, the latter has an advantage in that the piezoelectric elements can be built in the diaphragm by a relatively simple process in which a green sheet of piezoelectric material is put in accordance with the shape of the pressure generating chambers and then baked.
In such an ink jet recording head, a reservoir is generally formed as an ink chamber common to all the pressure generating chambers, so that ink is supplied to the respective pressure generating chambers through the reservoir.
In such an ink jet recording head, there is, however, the possibility that an inner surface constituting the reservoir may crack because the reservoir is provided with a partially mechanically ruptured portion. If such a reservoir filled with ink is used, a cracked portion of the inner surface of the reservoir may peel off as a broken piece. Hence, there is a problem that failure in ejection occurs because some nozzle orifice is choked with the broken piece.
In addition, a positioning hole or the like used for joining respective substrates is provided with a partially mechanically ruptured portion in the same manner as the reservoir. Hence, there is probability that failure in ejection may occur because of an alien substance such as a broken piece generated in the positioning hole.
It is therefore an object of the invention to provide a liquid jetting head, a method of manufacturing the same, and a liquid jetting apparatus incorporating the same, in which failure in ejection is prevented from being caused by an alien substance.
In order to achieve the above object, according to the present invention, there is provided a liquid jetting head, comprising:
a first substrate, which defines a plurality of pressure generating chambers, the first substrate including a vibration plate which forms a first surface of the first substrate, and formed with a first through hole;
a plurality of piezoelectric elements, each provided on the vibration plate so as to associate with one of the pressure generating chambers, each piezoelectric element comprised of an upper electrode, a lower electrode and a piezoelectric layer provided between the upper electrode and the lower electrode;
a second substrate, bonded onto at least the first surface of the first substrate, the second substrate formed with a second through hole communicated with the first through hole;
a communicating portion, at which the first through hole and the second through hole are connected; and
a laminated film, including a coating layer comprised of a resin material, the laminated film provided on an inner wall face of the communicating portion.
In this configuration, the coating layer contained in the laminated film fixes the other layers contained the laminated film. Hence, the laminated film is prevented from cracking. There is no broken piece generated because of breaking of the laminated film.
Preferably, the first through hole, the second through hole and the communicating portion serve as a reservoir which is a liquid chamber common to the pressure generating chambers.
In this configuration, failure in ejection can be prevented from being caused by some nozzle orifice choked with liquid contaminated with a broken piece of the laminated film.
Here, it is preferable that the laminated film is covered with a protective film comprised of a resin material.
In this configuration, a broken piece can be surely prevented from being generated because the laminated film is fixed by the protective film. In addition, the ink ejecting property is improved because ink flows smoothly.
Preferably, the first through hole, the second through hole and the communicating portion are serve as a positioning member.
In this configuration, there is no broken piece generated from the laminated film in the positioning member.
Preferably, the laminated film is formed on an outer peripheral face of a bonding surface of the first substrate and the second substrate.
In this configuration, an alien substance such as a broken piece can be prevented from being generated in the outer circumferential edge portion of the second substrate.
Preferably, the coating layer is comprised of an adhesive agent bonding the first substrate and the second substrate.
In this configuration, the coating layer can be relatively easily formed while the other layers contained in the laminated film are surely fixed by the coating layer.
Preferably, the coating layer is comprised of at least one of an epoxy-based resin, an acrylic-based resin, a urethane-based resin and a silicone-based resin.
In this configuration, when the coating layer is made of a predetermined material, the other layers contained in the laminated film can be surely fixed by the coating layer.
Preferably, the laminated film includes a part of layers forming the piezoelectric elements.
In this configuration, the laminated film can be relatively easily formed while the stiffness of the laminated film is improved because the laminated layer is constituted by a plurality of layers.
Preferably, the first substrate is comprised of a silicon monocrystalline substrate. Here, the pressure chambers and the first through hole are formed by etching process. The upper electrode, the lower electrode and the piezoelectric layer are formed by at least one of the film-forming process or a lithographic process.
In this configuration, a liquid jetting head having high-density nozzle orifices can be mass-manufactured relatively easily.
Here, it is preferable that a layer forming the laminated film which is the closest to the first substrate is comprised of an etching-resistant material.
In this configuration, the first through hole can be relatively easily formed by etching.
According to the present invention, there is also provided a liquid jetting apparatus comprising the above liquid jetting head.
In this case, there can be achieved a liquid jetting apparatus in which ink ejecting property of the head is stabilized to improve reliability.
According to the present invention, there is also provided a method of manufacturing a liquid jetting head, comprising the steps of:
providing a first substrate, which defines a plurality of pressure generating chambers, the first substrate including a vibration plate which forms a first surface of the first substrate, and formed with a first through hole;
forming a plurality of piezoelectric elements on the vibration plate so as to associate with one of the pressure generating chambers, each piezoelectric element comprised of an upper electrode, a lower electrode and a piezoelectric layer provided between the upper electrode and the lower electrode;
providing a second substrate formed with a second through hole;
bonding the second substrate onto the first surface of the first substrate with an adhesive agent, while forming a coating layer comprised of a resin material on an inner wall face of a region at which the first through hole and the second through hole are to be connected; and
forming a communicating portion at which the first through hole and the second through hole are connected.
In this configuration, the communicating portion is formed after the coating layer is formed. Hence, the inner wall portion of the communicating portion can be fixed by the coating layer to thereby prevent an alien substance such as a broken piece from being generated.
Preferably, the adhesive agent is extended so as to protruded from the inner wall face to form the coating layer.
In this configuration, the coating layer can be relatively easily formed, so that the manufacturing process can be simplified.
Preferably, the communicating portion is formed by a mechanical processing or a laser processing.
In this configuration, the communicating portion can be relatively easily formed.
Preferably, the manufacturing method further comprises the step of bonding a nozzle plate on a second surface of the first substrate opposing to the first surface, the nozzle plate formed with a plurality of nozzle orifices each communicated with one of the pressure generating chambers. Here, the bonding step of the nozzle plate is performed before the forming step of the communicating portion.
In this configuration, the stiffness of the first substrate is improved by the nozzle plate. Hence, the channel forming substrate can be prevented from cracking when the communicating portion is formed.
Preferably, the steps are performed with respect to a wafer in which a plurality of first substrates are integrally formed. The respective first substrates are divided after the forming step of the communicating portion.
Here, it is preferable that the coating layer is formed on an outer peripheral face of a bonding surface of each first substrate and an associated second substrate.
In this configuration, the wafer is divided along respective coating layers so that divided surfaces become relatively flat. Hence, an alien substance such as a broken piece can be restrained from being generated.
Preferably, the pressure chambers and the first through hole are formed by etching a silicon monocrystalline substrate. The upper electrode, the lower electrode and the piezoelectric layer are formed by at least one of the film-forming process or a lithographic process.
Preferably, the manufacturing method further comprises the step of covering the coating layer with a protective layer comprised of a resin material.